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Small molecule (not a peptide)Human trialsIn clinical trials

MK-677

Ibutamoren (MK-677)

Last reviewed October 27, 2026 · 26 sources · Written for general readers · Compare with another compound →

The bottom line

MK-677 is a pill, not a peptide, that copies the hunger hormone ghrelin and raises growth hormone and IGF-1. In trials it added some lean mass but did not improve strength or burn fat, it raised blood sugar, and it did not help people with Alzheimer's disease.[1][2] A hip fracture trial was stopped early over a heart failure warning sign, and FDA lists it among compounding substances with significant safety risks.[3][4] It is not approved, but a company is now testing it as LUM-201 in a Phase 3 trial in children with growth hormone deficiency.[5]

Where the evidence stands

What it is

MK-677, also called ibutamoren, is a small molecule taken by mouth. It is not a peptide. Its formula is C27H36N4O5S, and it is often made as a mesylate salt.[20]

Drug company scientists designed it in the 1990s as a pill that triggers growth hormone release, and it was tested in hundreds of people but never approved.[6][1][2]

A company now develops it under the code name LUM-201 as a possible daily pill for children with growth hormone deficiency. A Phase 3 placebo controlled trial started in May 2026.[12][5]

It is widely sold online as a research compound and grouped with SARMs, which are unapproved muscle building drugs. FDA says research only labels do not change that these are unapproved new drugs.[21] A European testing network found ibutamoren among the most common drugs in illegal sports enhancement products it seized over 5 years.[22]

FDA has also found it hidden, not listed on the label, in supplements marketed to help children grow taller.[23]

Name
MK-677 (Ibutamoren (MK-677))
Other names
ibutamoren, ibutamoren mesylate, MK-0677, L-163,191, LUM-201
Type
Small molecule (not a peptide)
CAS number
159634-47-6
Formula
C27H36N4O5S
Molecular weight
About 528.7 g/mol (free base)

What it does in the body

MK-677 is a lab made small molecule, not a peptide, designed by drug company chemists in the mid 1990s to be taken by mouth.[6] It switches on the growth hormone secretagogue receptor, the same receptor used by ghrelin, the body's natural hunger hormone, which sits in the pituitary gland and the hypothalamus of the brain.[7] Switching on that receptor makes the pituitary release larger pulses of the body's own growth hormone, which then raises IGF-1, a growth factor made mostly in the liver.[8]

This is the biology, area by area. A change measured in the body, like a higher blood level, does not always mean a person feels a benefit. The claims check below covers that.

Hormones

Measured in people

In healthy older adults, MK-677 roughly doubled 24 hour growth hormone by making natural pulses bigger, and IGF-1 rose about 88%, into the range of young adults.[8] IGF-1 rose about 40% in obese men, 55% to 94% in older adults and about 52% in young men with severe growth hormone deficiency.[9][10][11] In children in a trial, a single dose released nearly three times as much growth hormone as standard stimulation tests.[12] In dogs, cortisol rose about 2.4 fold, but in human studies cortisol, prolactin and thyroid hormones did not change significantly.[13][11]

Fat and appetite

Measured in people

Like ghrelin, it raises hunger. In a two year trial of 65 older adults, appetite rose and then faded within a few months, and body weight rose about 2.7 kg versus 0.8 kg on placebo.[1] In 24 obese men over 8 weeks, total and deep belly fat did not change, and resting calorie burn rose only briefly.[9]

Muscle and strength

Measured in people

In older adults, lean mass rose about 1.1 kg in a year while the placebo group lost about 0.5 kg, but strength and daily function did not improve.[1] In 8 young adults on a calorie cut diet, a week of MK-677 turned daily protein loss into a slight gain.[14]

Bones

Measured in people

In 105 frail older adults over 9 weeks, blood and urine markers of bone building rose about 10% to 29% and a marker of bone breakdown rose about 23%.[10] In 292 older women with osteoporosis, it raised bone turnover, and added to alendronate it raised hip neck bone density slightly more than alendronate alone, but not at the spine.[15] Higher turnover is not the same as stronger bones.

Sleep

Measured in people

In 8 young adults, a week on MK-677 increased deep sleep by about 50% and REM sleep by more than 20% compared with placebo. In 6 older adults without a placebo period, REM sleep rose nearly 50%.[16]

Blood sugar

Measured in people

In older adults over four weeks, fasting blood sugar rose about 26% in the strongest treatment group.[8] In the two year trial, fasting blood sugar rose slightly on average and insulin sensitivity fell.[1] In obese men, sugar handling on a glucose test got worse.[9]

Heart and blood vessels

Measured in people

In a trial of 123 older adults recovering from a broken hip, the trial was stopped early after a warning sign of heart failure in a few patients.[3] Mild leg swelling, a sign of fluid retention, was reported in the two year trial.[1] FDA cites the heart failure signal as a significant safety risk.[4]

How it works

MK-677 mimics ghrelin, a hormone that signals hunger and tells the pituitary gland to release growth hormone.[7][1]

  • It binds the growth hormone secretagogue receptor found in the pituitary and the hypothalamus. It works through a different path than growth hormone releasing hormone, the target of sermorelin and tesamorelin.[7][6]
  • In older adults, it raised growth hormone mainly by making natural pulses bigger, not more frequent, and brought IGF-1 into the range typical of young adults.[8]
  • In people with Alzheimer's disease, it raised IGF-1 by about 60% to 73%.[2]
  • Like ghrelin, it increases appetite.[1]
  • It also makes the body handle sugar less well, which shows up as higher fasting blood sugar and lower insulin sensitivity.[8][1]

The hormone changes are well measured in people. Whether they lead to real health benefits has not been shown.

What the research shows

We keep animal and human evidence apart. A result in animals is a reason to study something in people, not proof that it works in people.

Animal and lab studies

Dog studies showed a large, long growth hormone rise

  • In rat pituitary cells in a dish, it released growth hormone at very low concentrations, and in dogs it raised growth hormone when taken by mouth without changing several other hormones.[6]
  • In beagles, a single dose by mouth raised peak growth hormone up to about 16 times, and levels stayed high for up to 6 hours, a longer response than older growth hormone releasing peptides.[13]
  • In the same dogs, IGF-1 rose about 30%, cortisol rose about 2.4 times, and prolactin did not change. Insulin and blood sugar went up but stayed in the normal range.[13]
  • Because MK-677 has been tested in hundreds of people in placebo controlled trials, the human results matter more than the animal work.[1][2]

Limit: Dog studies show how the drug acts, not whether it is safe or useful in people.

Human studies

Raises hormones and lean mass, but no proven health benefit

  • In 32 healthy adults aged 64 to 81 given a daily pill or placebo for up to 4 weeks, the strongest treatment group roughly doubled 24 hour growth hormone, IGF-1 rose about 88%, and fasting blood sugar rose about 26%.[8]
  • In 9 young men with severe growth hormone deficiency since childhood, four days of the pill in a placebo controlled crossover raised average 24 hour growth hormone in every man and IGF-1 about 52%. It was described as well tolerated.[11]
  • In 8 healthy young adults on a calorie cut diet, one week on MK-677 turned daily protein loss into a slight gain, while protein loss continued on placebo.[14]
  • In 24 obese men aged 18 to 50 over 8 weeks, IGF-1 rose about 40% and fat free mass rose, but total and deep belly fat did not change. Sugar handling on a glucose test got worse.[9]
  • In 8 young adults, a week on MK-677 increased deep sleep by about 50% and REM sleep by more than 20% compared with placebo.[16]
  • In a two year trial of 65 healthy adults aged 60 to 81, people on MK-677 gained about 1.1 kg of lean mass after one year, while the placebo group lost about 0.5 kg. Strength and daily function did not improve. Appetite rose and faded, mild leg swelling and muscle pain were reported, and insulin sensitivity fell.[1]
  • In 187 older adults across three placebo controlled studies of 2 to 9 weeks, markers of bone building and breakdown rose, up to about 29% for one bone building marker in frail elders.[10] In 292 older women with osteoporosis over 12 to 18 months, combined with alendronate it improved hip neck bone density a bit more than alendronate alone (4.2% versus 2.5%), but not at the spine or whole hip.[15]
  • In a one year trial of 563 people with mild to moderate Alzheimer's disease, MK-677 did not slow decline on any memory or daily living measure.[2]
  • In 161 adults aged 65 and over after hip fracture, six months on the pill raised IGF-1 by 84% versus 17% on placebo, but function and independent living did not improve significantly.[17] A second trial of 123 patients found a small gain on one walking score and was stopped early after a warning sign of heart failure in a few patients.[3]
  • In 18 children with growth hormone deficiency, about a week of the drug raised growth hormone and IGF-1 without significant changes in cortisol, thyroid hormones or blood sugar.[18] In a later trial of 68 children, a single dose released a median of nearly three times as much growth hormone as standard tests.[12]

Limit: Trials were mostly in older or sick adults, none tested bodybuilding or anti aging use, and the longest lasted two years.

Claims check

The most common claims about this compound, and what studies actually found. Verdicts rate the evidence, not whether you should use it.

Raises growth hormone and IGF-1

Shown in people

Several placebo controlled trials found it raises both. IGF-1 rose about 40% in 24 obese men, 39% to 45% in 292 older women, 84% in 161 people after hip fracture and 60% to 73% in 563 people with Alzheimer's disease.[9][15][17][2]

Builds muscle

Mixed results

Lean mass rose about 1.1 kg over a year in 65 older adults and fat free mass rose in 24 obese men over 8 weeks.[1][9] But strength and daily function did not improve in the older adults.[1]

Burns fat

No benefit in trials so far

In 24 obese men over 8 weeks, total and deep belly fat did not change compared with placebo.[9] In older adults, body weight rose about 2.7 kg in a year versus 0.8 kg on placebo.[1]

Increases appetite and helps weight gain

Shown in people

In a two year placebo controlled trial of 65 older adults, appetite rose, mainly in the first months, and weight rose about 2.7 kg versus 0.8 kg on placebo.[1] It works on the same receptor as ghrelin, the body's hunger hormone.[7]

Improves sleep

Mixed results

In one small study, 8 young adults had about 50% more deep sleep and over 20% more REM sleep after a week compared with placebo, and 6 older adults had more REM sleep.[16] No larger trial has confirmed this.

Strengthens bones

Mixed results

In 187 older adults, MK-677 raised markers of both bone building and bone breakdown over 2 to 9 weeks.[10] In 292 older women with osteoporosis, added to alendronate it raised hip neck bone density slightly more than alendronate alone. It did not improve density at the spine, whole hip or whole body.[15]

Protects the aging brain

No benefit in trials so far

In a one year placebo controlled trial of 563 people with Alzheimer's disease, it raised IGF-1 but did not slow decline in memory or daily living.[2]

Speeds recovery from injury

Mixed results

In 161 older adults after a broken hip, six months of MK-677 raised IGF-1 but did not significantly improve function or independent living.[17] A later trial of 123 hip fracture patients found a small but significant gain in walking speed, no gain on most other function tests, and was stopped early over a heart failure signal.[3] In dieting young adults it reduced protein loss for one week.[14]

Helps children grow taller

Mixed results

In 18 children with growth hormone deficiency, about a week of MK-677 raised growth hormone and IGF-1, but growth was not measured.[18] In a trial of 68 children, growth over 6 months was better in children whose glands still responded well to the drug, while children without those markers did better on standard growth hormone shots.[19] A Phase 3 trial of 150 children is now testing it against placebo.[5]

Known risks and side effects

  • Heart failure signal. A hip fracture trial was stopped early over possible heart failure, and FDA cites this as a significant safety risk.[3][4]
  • Higher blood sugar. Fasting blood sugar rose about 26% within four weeks in one study of older adults, and insulin sensitivity fell in the two year trial.[8][1] FDA lists changes in sugar handling as a concern.[23]
  • Hunger, swelling and muscle pain. Stronger appetite, mild leg swelling and muscle pain were reported in the two year trial, and FDA also lists water retention and fatigue.[1][23]
  • Hidden in supplements. FDA found unlabeled ibutamoren in growth supplements sold for children, so people may take it without knowing.[23]
  • Unregulated online products. MK-677 sold online is an unapproved drug with no FDA check on purity, strength or contamination, whatever its label says.[21] European labs found it among the most common drugs in seized sports enhancement products, and most samples tested held active amounts, some even more.[22] WADA bans it at all times.[24][25]

Regulatory status

Today: MK-677 is not FDA approved. Under the name LUM-201 it is in a Phase 3 placebo controlled trial in children with growth hormone deficiency that began in May 2026, which is why we list it as investigational.[5] FDA lists ibutamoren mesylate in Category 2, its group of compounding substances that raise significant safety risks, citing possible heart failure.[4][26] WADA names ibutamoren as banned at all times on both its 2026 and 2027 lists.[24][25]

  1. Scientists publish the design of MK-0677 and select it for human studies.[6]
  2. Results of the two year trial in older adults and the Alzheimer's trial were published.[1][2]
  3. The hip fracture trial was published, noting it had been stopped early for a heart failure signal.[3]
  4. FDA placed ibutamoren mesylate in Category 2 for outsourcing facilities (503B).[4]
  5. FDA placed ibutamoren mesylate in Category 2 for compounding pharmacies (503A).[4]
  6. FDA sent warning letters over products containing MK-677, including children's growth supplements with hidden ibutamoren.[21][23]
  7. A Phase 3 trial of the drug as LUM-201 in 150 children with growth hormone deficiency starts enrolling.[5]
  8. The 2027 WADA list, which keeps ibutamoren banned, takes effect.[25]

Sources

  1. Nass R, Pezzoli SS, Oliveri MC, Patrie JT, Harrell FE Jr, Clasey JL, et al. Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial. Ann Intern Med. 2008;149(9):601-611. PMID 18981485
  2. Sevigny JJ, Ryan JM, van Dyck CH, Peng Y, Lines CR, Nessly ML; MK-677 Protocol 30 Study Group. Growth hormone secretagogue MK-677: no clinical effect on AD progression in a randomized trial. Neurology. 2008;71(21):1702-1708. PMID 19015485
  3. Adunsky A, Chandler J, Heyden N, Lutkiewicz J, Scott BB, Berd Y, et al. MK-0677 (ibutamoren mesylate) for the treatment of patients recovering from hip fracture: a multicenter, randomized, placebo-controlled phase IIb study. Arch Gerontol Geriatr. 2011;53(2):183-189. PMID 21067829
  4. U.S. Food and Drug Administration. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks. Content current as of April 22, 2026. FDA
  5. ClinicalTrials.gov. A multicenter, 12-month, randomized, double-blind, placebo-controlled Phase 3 efficacy and safety study of daily oral LUM-201 in treatment-naive, prepubertal children with growth hormone deficiency (NCT06948214). Sponsor Lumos Pharma. Last update posted August 6, 2026. NCT06948214
  6. Patchett AA, Nargund RP, Tata JR, Chen MH, Barakat KJ, Johnston DB, et al. Design and biological activities of L-163,191 (MK-0677): a potent, orally active growth hormone secretagogue. Proc Natl Acad Sci U S A. 1995;92(15):7001-7005. PMID 7624358
  7. Howard AD, Feighner SD, Cully DF, Arena JP, Liberator PA, Rosenblum CI, et al. A receptor in pituitary and hypothalamus that functions in growth hormone release. Science. 1996;273(5277):974-977. PMID 8688086
  8. Chapman IM, Bach MA, Van Cauter E, Farmer M, Krupa D, Taylor AM, et al. Stimulation of the growth hormone (GH)-insulin-like growth factor I axis by daily oral administration of a GH secretogogue (MK-677) in healthy elderly subjects. J Clin Endocrinol Metab. 1996;81(12):4249-4257. PMID 8954023
  9. Svensson J, Lönn L, Jansson JO, Murphy G, Wyss D, Krupa D, et al. Two-month treatment of obese subjects with the oral growth hormone (GH) secretagogue MK-677 increases GH secretion, fat-free mass, and energy expenditure. J Clin Endocrinol Metab. 1998;83(2):362-369. PMID 9467542
  10. Murphy MG, Bach MA, Plotkin D, Bolognese J, Ng J, Krupa D, Gertz BJ. Oral administration of the growth hormone secretagogue MK-677 increases markers of bone turnover in healthy and functionally impaired elderly adults. J Bone Miner Res. 1999;14(7):1182-1188. PMID 10404019
  11. Chapman IM, Pescovitz OH, Murphy G, Treep T, Cerchio KA, Krupa D, et al. Oral administration of growth hormone (GH) releasing peptide-mimetic MK-677 stimulates the GH/insulin-like growth factor-I axis in selected GH-deficient adults. J Clin Endocrinol Metab. 1997;82(10):3455-3463. PMID 9329386
  12. Bright GM, Thorner MO. A GH Secretagogue Receptor Agonist (LUM-201) Elicits Greater GH Responses than Standard GH Secretagogues in Subjects of a Pediatric GH Deficiency Trial. Horm Res Paediatr. 2022;95(1):76-81. PMID 35354138
  13. Jacks T, Smith R, Judith F, Schleim K, Frazier E, Chen H, et al. MK-0677, a potent, novel, orally active growth hormone (GH) secretagogue: GH, insulin-like growth factor I, and other hormonal responses in beagles. Endocrinology. 1996;137(12):5284-5289. DOI 10.1210/endo.137.12.8940347
  14. Murphy MG, Plunkett LM, Gertz BJ, He W, Wittreich J, Polvino WM, Clemmons DR. MK-677, an orally active growth hormone secretagogue, reverses diet-induced catabolism. J Clin Endocrinol Metab. 1998;83(2):320-325. PMID 9467534
  15. Murphy MG, Weiss S, McClung M, Schnitzer T, Cerchio K, Connor J, Krupa D, Gertz BJ. Effect of alendronate and MK-677 (a growth hormone secretagogue), individually and in combination, on markers of bone turnover and bone mineral density in postmenopausal osteoporotic women. J Clin Endocrinol Metab. 2001;86(3):1116-1125. PMID 11238495
  16. Copinschi G, Leproult R, Van Onderbergen A, Caufriez A, Cole KY, Schilling LM, et al. Prolonged oral treatment with MK-677, a novel growth hormone secretagogue, improves sleep quality in man. Neuroendocrinology. 1997;66(4):278-286. PMID 9349662
  17. Bach MA, Rockwood K, Zetterberg C, Thamsborg G, Hebert R, Devogelaer JP, et al. The effects of MK-0677, an oral growth hormone secretagogue, in patients with hip fracture. J Am Geriatr Soc. 2004;52(4):516-523. PMID 15066065
  18. Codner E, Cassorla F, Tiulpakov AN, et al. Effects of oral administration of ibutamoren mesylate, a nonpeptide growth hormone secretagogue, on the growth hormone-insulin-like growth factor I axis in growth hormone-deficient children. Clin Pharmacol Ther. 2001;70(1):91-98. PMID 11452249
  19. Bright GM, Do MT, McKew JC, Blum WF, Thorner MO. Development of a Predictive Enrichment Marker for the Oral GH Secretagogue LUM-201 in Pediatric Growth Hormone Deficiency. J Endocr Soc. 2021;5(6):bvab030. PMID 33982679
  20. U.S. FDA and NCATS Global Substance Registration System (GSRS). Ibutamoren, UNII GJ0EGN38UL. FDA GSRS
  21. U.S. Food and Drug Administration. Warning letter to Prime Sports Nutrition (MARCS-CMS 719433). December 12, 2025. FDA warning letter
  22. Mendoza Barrios M, Deconinck E, Vanhee C, Lamme EK, 't Hart-Bakker I, Syversen PV, et al. SARMs, Metabolic Modulators and Growth Hormone Secretagogues in Suspected Illegal Medicines, Bought as Sport Performance Enhancers: A Retro- and Prospective Study Within the GEON. Drug Test Anal. 2025;17(10):2078-2085. PMID 40551438
  23. U.S. Food and Drug Administration. Warning letter to Agebox Inc. (MARCS-CMS 718252). December 19, 2025. FDA warning letter
  24. World Anti-Doping Agency. The 2026 Prohibited List, section S2.2.4 Growth hormone releasing factors. In force January 1, 2026. WADA 2026
  25. World Anti-Doping Agency. The 2027 Prohibited List. Comes into effect 1 January 2027. WADA 2027 List
  26. U.S. Food and Drug Administration. Bulk Drug Substances Nominated for Use in Compounding Under Section 503A of the FD&C Act (categories list). Updated May 14, 2026. FDA 503A categories
Medical disclaimer

This page is educational information only. It is not medical advice and does not replace care from a licensed medical provider. Do not use this page to decide whether to take any substance. Talk to a licensed medical provider first.

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